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Subject[PATCH 6/7] x86/jump lables: Show where and what was wrong on errors
From: Steven Rostedt <srostedt@redhat.com>

When modifying text sections for jump labels, a paranoid check is
performed. If the check fails, the system "bugs". But why it failed
is not shown.

The BUG_ON()s in the jump label update code is replaced with bug_at(ip).
This is a function that will show what pointer failed, and what was
at the location of the failure that made jump label panic.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/kernel/jump_label.c | 31 +++++++++++++++++++++----------
1 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index d426da6..9bae2c9 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -32,6 +32,18 @@ union jump_code_union {
} __packed;
};

+static void bug_at(unsigned char *ip, int line)
+{
+ /*
+ * The location is not an op that we were expecting.
+ * Something went wrong. Crash the box, as something could be
+ * corrupting the kernel.
+ */
+ printk("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n",
+ ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line);
+ BUG();
+}
+
static void __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
void *(*poker)(void *, const void *, size_t),
@@ -59,12 +71,7 @@ static void __jump_label_transform(struct jump_entry *entry,
code.jump = 0xe9;
code.offset = entry->target - (entry->code + size);
} else
- /*
- * The location is not a nop that we were expecting,
- * something went wrong. Crash the box, as something could be
- * corrupting the kernel.
- */
- BUG();
+ bug_at(ip, __LINE__);
} else {
/*
* We are disabling this jump label. If it is not what
@@ -78,7 +85,8 @@ static void __jump_label_transform(struct jump_entry *entry,
return;

/* We are initializing from the default nop */
- BUG_ON(memcmp(ip, default_nop, 5) != 0);
+ if (unlikely(memcmp(ip, default_nop, 5) != 0))
+ bug_at(ip, __LINE__);

/* Set to the ideal nop */
size = JUMP_LABEL_NOP_SIZE;
@@ -91,7 +99,9 @@ static void __jump_label_transform(struct jump_entry *entry,
code.jump = 0xe9;
code.offset = entry->target -
(entry->code + JUMP_LABEL_NOP_SIZE);
- BUG_ON(memcmp(ip, &code, 5) != 0);
+
+ if (unlikely(memcmp(ip, &code, 5) != 0))
+ bug_at(ip, __LINE__);

size = JUMP_LABEL_NOP_SIZE;
memcpy(&code, ideal_nops[NOP_ATOMIC5], size);
@@ -101,13 +111,14 @@ static void __jump_label_transform(struct jump_entry *entry,
/* Had better be a 2 byte jmp */
code.jump_short = 0xeb;
code.offset = entry->target - (entry->code + 2);
- BUG_ON(memcmp(ip, &code, 2) != 0);
+ if (unlikely(memcmp(ip, &code, 2) != 0))
+ bug_at(ip, __LINE__);

size = 2;
memcpy(&code, nop_short, size);
} else
/* The code was not what we expected! */
- BUG();
+ bug_at(ip, __LINE__);
}

(*poker)(ip, &code, size);
--
1.7.8.3

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